This invention relates in general to non-contact sensing of features of solids and liquids and, more specifically, to a laser beam system for sensing distance to an object, the identification and locating of interfaces between different liquids or of particles in a liquid and the determination of other physical features.
Precise measurement of distances to objects, in particular inaccessible objects, has long been accomplished by triangulation using trigonometric functions. Typically, two mirrors along a base normal to the line of sight to the object are adjusted to provide a single image. The distance to the object can be calculated using the mirror angles and the base length. Such rangefinders have had extensive application in cameras, artillery rangefinding and the like.
A number of different devices have been developed using triangulation techniques, such as those described by Z. Ji and M. C. Leu, "Design of Optical Triangulation Devices". Optical & Laser Technology, Vol. 21, No. 5, 1989. Applications of triangulation distance measurement include cameras as described by Misawa et al. in U.S. Pat. No. 5,274,429, and by Higaki et al. in U.S. Pat. No. 5,253,032, long range distance measurement as described by Beder et al. in U.S. Pat. No. 5,057,681 and by Ryczek in U.S. Pat. No. 5,055,664 and others. The prior triangulation devices generally use position sensitive devices as the reflected light detectors for the reflected light which limits system accuracy and application potential. Accuracy at long distances is lost unless a high base-to-object distance ratio is used. With very long bases, stable mechanical coordination of the light emitter and detector is difficult.
These prior triangulation and position sensitive devices and methods also suffer from a limited target range and target depth capability and are generally only capable of detecting a single target at any given moment.
Thus, there is a continuing need for improved systems for more accurately measuring distances over an expanded range of distances, for simultaneously detecting a large number of targets, such as particles in a liquid and for observing dynamic behavior of particles or liquid interfaces in real time.